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Title: The evolution of Fermi liquid interactions in Sr2RuO4 under pressure
Author: Forsythe, D.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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There is strong evidence that a common pairing mechanism is in operation in many classes of unconventional superconductor that is related to the proximity of a magnetic quantum critical point. Hydrostatic pressure has been shown to be an effective means to tune systems near to quantum critical regions and some of the most convincing evidence linking superconductivity to magnetism has emerged from such experiments. In this work, we describe the development of a unique system that couples this high pressure tuning technique with the powerful normal state probe of quantum oscillations, in order to test models of superconductivity that make quantitative predictions regarding the normal state. As a first application, we examine how the quantum oscillation spectrum of the exotic superconductor Sr2RuO4 evolves up to pressures in excess of 30 kbar and through a region in the phase diagram previously thought to contain a quantum critical point. Combining these experiments with conventional low field measurements of the T2 A-coefficient of the resistivity and the upper critical field, we discuss the implications of our new results to possible pressure phase diagrams in the context of the "Magnetic Interaction Model", and adaptation of BCS theory to magnetic interactions. As an extension, by analysing interference effects in the oscillation spectra, we have been able to extract extremely accurate values for cylindrically symmetric contributions to the c-axis dispersion in Sr2RuO4. Access to the total warping is restricted for the α and β sheets, but we find a striking reduction under pressure in the warping of the γ sheet, which is thought to be the active band in orbital dependent theories of superconductivity. In such a scenario, this indicates a reduction in the coupling between the active and passive bands. More generally, it implies a reduced effective dimensionality in the γ sheet, which might act to suppress superconductivity via fluctuation effects.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available